CAIRO, Jan 22 (Reuters) - Egypt's pound weakened to 7.39 per dollar from 7.34 the previous day at a central bank auction on Thursday, the weakest level it has been allowed to reach since auctions began in December 2012 and the fifth official depreciation this week.

The bank offered 40 million dollars and sold 38.4 million at a cutoff price of 7.3901 pounds per dollar, the central bank said.

The rates at which banks are allowed to trade dollars are determined by the results of central bank sales, giving the bank effective control over official exchange rates, though there remains an active black market in the pound. (Reporting by Maggie Fick; Editing by Alison Williams)